We understand your frustration about being unable to access your account using the Quickbooks Online mobile App @Mark11_2. Please know that I'll be here to help you how to fix this error you encountered.
Let's resolve the issue by refreshing data to help your QuickBooks Mobile app update the latest information.
For Android:
Select Settings and tap the Refresh Data option.
Click Yes to confirm the action.
For iOS:
Go to the menu or the three horizontal lines icon.